Expandable graphite intercalation compounds are also known as expanding graphite and are commercially available. They are compounds, which contain foreign components intercalated between the lattice layers of the graphite. Such expandable graphite intercalation compounds usually are prepared by dispersing graphite particles in a solution, which contains an oxidizing agent and a guest compound, which is to be intercalated. Usually, nitric acid, potassium chlorate, chromic acid, potassium permanganate and the like are used as oxidizing agent. Concentrated sulfuric acid, for example, is used as compound, which is to be intercalated, the reaction taking place at temperatures of 60° C. to 130° C. during a period of up to four hours (see, for example, EP-B-0 085 121). Alternatively, it is also possible to intercalate metal chlorides in the graphite in the presence of, for example, chlorine gas (E. Stumpp. Physics (1981, 9–16).
The expandable graphite intercalation compounds or expanding graphites experience a large increase in volume when heated to a temperature above the so-called onset temperature. The expansion factor is more than 200 and is caused owing to the fact that the intercalation compounds, intercalated in the layer structure of the graphite, are decomposed by the rapid heating to this temperature with formation of gaseous materials, as a result of which the graphite particles are expanded perpendicularly to the plane of the layers (EP-B-0 085 121). This expansion behavior is utilized in intumescing compositions, which are used, for example, for sealing cable and pipe wall bushings through walls and ceilings of buildings as fire protection. In the event of a fire, after the onset temperature has been reached, the graphite particles and, with that, the intumescing composition sealing the wall bushings, expand so that, in even after the cable and/or the plastic pipes, passed through the wall bushings, have been burned completely, the fire is prevented or delayed from breaking through the wall bushing.
The onset temperature is defined as the temperature, at which the thermal expansion process of the intumescing system, that is, of the expandable graphite intercalation compound, commences. In other words, it is the temperature at the start of the expansion process. The conventional, commercially obtainable types of expanding graphite have very limited onset temperatures of about 150° C., about 160° C. and about 200° C. In order to be able to react flexibly to special product requirements with respect to the intumescing behavior for the production of fire-protection compositions, expandable, graphite intercalation compounds are required which have a greater range of variation with regard to their onset temperature.